1. Field of the Invention
The invention relates to an optical multi-layer system on a crystalline substrate, which is obtainable by a one-stage baking process (“stack cure”), to a process for producing the optical multi-layer system and to its use.
2. Discussion of Background Information
Apart from by means of sputtering and vapor deposition processes, multi-layer systems with optical properties can be produced on glass by means of the so-called sol-gel process; see, for example, Dislich et al. DE 1941191. The principle of this production method is that the appropriate glass substrate is coated with a sol by a dipping process and the layer is dried and baked at relatively high temperatures in order to achieve consolidation. The pre-drying at relatively high temperatures is necessary in order to impart to the first layer sufficient chemical stability, since it is otherwise dissolved partly or fully by the new coating sol. The process is complicated, since a thermal treatment at temperatures of 400-500° C. is required after each layer application. This makes the production of multi-layer systems, as required in specific optical applications (broadband antireflection coating, cold light mirror, etc.), exceptionally labor-intensive and costly.
P. W. Oliveira, H. Krug, A. Frantzen, M. Mennig, H. Schmidt describe, in SPIE, vol. 3136, pages 452-461, a process for producing optical multi-layer systems on plastics substrates using nanoscale particles surface-modified with 3-glycidyloxypropyltrimethoxysilane in an organically modified inorganic matrix. Photolytic curing is effected. A thermal treatment is effected up to a maximum of 80° C. This allows interference layer systems to be produced on plastics substrates.
WO 99/61383 describes a process for producing optical multi-layer systems on glass substrates, in which at least two coating compositions which comprise nanoscale inorganic solid particles having polymerizable and/or polycondensable organic surface groups are applied to a glass substrate and baked in one stage.
The wet-chemical optical multi-layer systems obtained in accordance with the prior art are based on a glass or plastics substrate.